Atmospheric chemistry of 1,2-dichloroethane: UV spectra of CH2ClCHCl and CH2ClCHClO2 radicals, kinetics of the reactions of CH2ClCHCl radicals with O-2 and CH2ClCHClO2 radicals with NO and NO2, and fate of the alkoxy radical CH2ClCHClO

A pulse radiolysis technique was used to measure the UV absorption spectra of CH2ClCHCl and CH2ClCHClO2 radicals over the range 230-300 nm. At 250 nm, sigma(CH2ClCHCl) = (1.7 +/- 0.2) x 10(-18) and sigma(CH2ClCHClO2) = (3.5 +/- 0.5) x 10(-18) cm(2) molecule(-1). The observed self-reaction rate constant for CH2ClCHCl radicals, defined as -d[CH2ClCHCl]/dt = 2k(4)[CH2ClCHCl](2) was k(4) = (2.0 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1). The rate constant for reaction of CH2ClCHCl radicals with O-2 in one bar of SF6 diluent was (2.4 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1). The rate constants for the reactions of CH2ClCHClO2 radicals with NO and NO2 were k(5) greater than or equal to 9 X 10(-12) and k(6) = (9.8 +/- 0.6) x 10(-12) cm(3) molecule(-1) s(-1), respectively. The rate constant for the reaction of F atoms with CH2ClCH2Cl was k(3) = (2.6 +/- 0.2) x 10(-11) cm(3) molecule(-1) s(-1). The reaction of CH2ClCHClO2 radicals with NO produced NO2 and, by implication, CH2ClCHClO radicals. A FTIR spectroscopic technique showed that CH2ClCHClO radicals undergo both reaction with O-2 and decomposition via intramolecular 3-center HCl elimination. In 700 Torr of air at 296 K the rate constant ratio k(O2)/k(decomp) = (2.3 +/- 0.2) x 10(-20) cm(3) molecule(-1). A lower limit of 4 x 10(5) s(-1) was deduced for the rate of intramolecular 3-center HCl elimination from CH2ClCHClO radicals at 296 K in 1 bar of SF6 diluent. As part of this work a relative rate technique was used to measure rate constants of (1.3 +/- 0.2) x 10(-12) and (6.4 +/- 1.4) x 10(-14) cm(3) molecule(-1) s(-1) for the reactions of Cl atoms with CH2ClCH2Cl and CH2ClC(O)Cl, respectively. All experiments were performed at 296 K. Results are discussed in the context of the atmospheric chemistry of 1,2-dichloroethane.